A pull-open locking device for doors of electrical domestic appliances, in which the safety circuit is mechanically in direct active contact with the locking device, is described in DE 33 01 636 C2. With this is known device, a pivoting forked latch, which can be brought into a stable open or closed position by means of a bolt permanently fixed in the unit housing when the door is opened and closed, is arranged in the door. The movement of the forked latch is transmitted in the manner of a toggle joint via a spring-loaded push rod to a plunger, which actuates a switch located in the electrical circuit of the domestic appliance. The functional elements of this combined locking and safety circuit are adjusted so that, when opening the door, the mains circuit of the unit is interrupted when the balance point of the toggle joint is overcome by the pulling-open movement.
The locking device is accommodated pre-mounted in a lock housing, which is set into a carrier plate in the door.
Devices of the kind described in which the safety circuit is mechanically coupled to the pull-open door catch have not become established in practice due to their susceptibility to failure. Devices have become known in a multitude of different embodiments in which the door catch and the safety circuit for the mains voltage are functionally separate from one another. A variant of a solution, which is frequently encountered in practice, provides that the switching circuit is actuated by a spring-loaded plunger, which protrudes from the front wall of the domestic appliance when the door is in the open position and which is pressed inwards by the door frame when the door is closed. The plunger is usually centrally arranged in the top part of the loading opening and therefore also spatially separate from the door catch. It is also known to arrange the plunger fixed to the door frame.
Associated with this arrangement of the plunger is the advantage that, in the event of a possible change of door hinging, the switching device works in the same way for both hinging possibilities without modification work.
Locking and switching device are adjusted so that the switching contacts of an interrupt switch located in the mains circuit of the unit are closed in the closed position of the door, and these open due to the effect of spring pressure when the door frame is lifted away from the closed position by a pulling-open movement and releases the plunger.
In the course of time, the door can warp, possibly through ageing or through improper use of the domestic appliance. It is then disadvantageous that the adjustment made by the manufacturer of the unit between the locking and switching device is lost and, as a result of this, faults can occur in the safety circuit. The switch contacts are then namely no longer able to close reliably when the door is closed, for example, or at best the power supply for the unit is only interrupted with a delay when the door is opened.